The present invention relates to a space switch matrix for electrical signals, in particular but not exclusively for switching microwave or radio frequency signals.
Switching matrices for microwave or radio frequency signals are well known and have been implemented previously in a number of ways. For example U.S. Pat. No. 3,833,866 discloses an arrangement for an m×n switch matrix which comprises m (1×n) power dividers, n (1×m) power combiners and m×n switched transmission lines connecting each output arm of the dividers with each input arm of the combiners. Such an arrangement is depicted in FIG. 1 for the example case of an 8×8 switch matrix. It comprises 1:8 power dividers 1 on each of the 8 input ports, 8:1 power combiners 2 on each of the 8 output ports and 64 interconnecting transmission lines 3 each containing a terminated on-off switch 4.
This type of switch matrix allows any input port to be connected to any output port. It also allows any combination of input ports to be connected to any combination of output ports and so can be used in a number of modes including broadcast. U.S. Pat. No. 3,833,866 discloses an arrangement where a large switch matrix is constructed using a set of interconnected circuit boards. For example an 8×8 switch matrix would be constructed using 8 input circuit boards containing power dividers and 8 perpendicularly mounted output circuit boards containing power combiners, at least one of the boards also containing on-off switches. However, this approach is difficult to implement with acceptable size, cost and performance.
The present invention discloses a means of reducing the size and insertion loss while at the same time increasing the isolation and return loss of a microwave switch matrix for a given bandwidth compared to prior art designs.